I did a search on my question and did not find anything close to my situation. Last year my 1991 300D began making a loud ticking noise that kept getting worse. When the engine was cold there was no noise but after the engine heated up the ticking would start. I changed the timing chain and the tick was still there. It turned out to be the vacuum pump. Here it is a year later and that same sound is starting again. Am I doing something wrong? What could be causing a noisey pump?

Thanks

Did you inspect and replace the injection timer at the time the vacuum pump was R&R'd? In many cases the eccentric cam that drives the pump roller can become scored, which will radically shorten the life of the new pump. I would get on this problem ASAP, before the pump roller becomes far too damaged and grenades, taking out the timing chain--really!

Thanks for the reply! I didn't do the work so I'll have to ask the mechanic who did. He seemed to know what he was doing.

This is a reasonably common issue. I recently purchased an injection pump for an OM603 engine with the injection timer still attached. It's eccentric cam was deeply gouged and the t-chain teeth were all chewed up, which leads me to believe the vacuum pump disintegrated and took out the t-chain/engine.